Medicaid is a joint federal and state health insurance program that today covers 72.5 million low-income individuals and people with disabilities in the U.S. Prior to the Affordable Care Act, Medicaid predominantly covered low-income children, pregnant women and individuals with disabilities. The 2010 Affordable Care Act expanded Medicaid eligibility to low-income adults earning up to 138% of the federal poverty level ($16,753 for a single individual, $34,638 for a family of four in 2018). Millions of families residing in low-income communities obtained health care coverage under Medicaid expansion, which has been adopted by 32 states. Many impacts have been attributed to Medicaid expansion, including positive impacts on several risk factors that directly contribute to child and family wellbeing, including parent and child mental health problems and substance misuse, and family financial instability. Parental depression, parent and youth substance misuse, and family financial stress are robust risk factors for child abuse and neglect, youth violence, and intimate partner violence. Thus, an investigation of the violence prevention effects of Medicaid expansion is warranted and timely. We propose the first evaluation of Medicaid expansion policy on the prevention of child abuse and neglect, youth violence, and intimate partner violence. The aims of this study include evaluating the impact of Medicaid expansion on reported and substantiated cases of child abuse and neglect (Aim 1), on youth violent crime reports, charges, and adjudications (Aim 2), and on intimate partner violence perpetration (Aim 3). Our study takes advantage of publically available national databases that provide information on child abuse and neglect reports and substantiations and on reports of intimate partner violence as well as relationships with several state agencies to obtain non-public juvenile justice records. Our 12-year study period is January 1, 2008-December 31, 2019. This period ensures that we can track study outcomes (e.g., rates of child abuse and neglect) for about six years prior to Medicaid expansion (which took effect in 2014) and six years after expansion. We will compare outcomes within states that chose to expand Medicaid and between states that did/did not choose to expand Medicaid. We hypothesize that violence will have declined following policy implementation in states that expanded Medicaid and also relative to states that did not expand Medicaid. In the proposed study, we will use an analytic approach called ?CITS? to conduct these comparisons. Study results will advance understanding of what works to prevent violence in low-income communities and, more specifically, provide the public, policy makers, and other stakeholders with objective information regarding the complementary effects of Medicaid expansion on the primary prevention of violence. Results will be of particular relevance to policy makers in the 18 states that did not expand Medicaid, many of whom are actively considering adoption of this policy.